The present invention relates to a process for recovering silver and other metal from stainless steel sections from military aircraft which are brazed with a silver based brazing compound.
It is necessary in supersonic military aircraft that certain parts including flaps, ailerons and engine supporting struts are made of stainless steel rather than aluminum and the other metals and alloys used in the rest of the aircraft because of the high temperatures and stresses to which they are subjected. The stainless steel sections comprise contoured outer sheets with inner support fabricated as honeycomb sections. The honeycomb sections are brazed to the contoured outer sheets with a silver based brazing compound.
When these military aircraft are declared obsolete and discarded for scrap the silver-brazed stainless steel sections are separated from the rest of the aircraft for separate recovery of the metals therein or other scrapping procedures. These silver brazed stainless steel sections contain approximately 5 to 30 weight percent silver and 2 to 15 weight percent copper, balance stainless steel.
Previous methods used for electrolytic recovery of silver have not been able to be used to recover silver from metals containing low percentages of silver. For example, the Moebius cell needs a silver concentration in the anodes of greater than 95% and the Thum or Balbach systems can accept any refinable metal whose silver content exceeds 75%. (Non-Ferrous Extractive Metallurgy in the U.K., W. Ryan (Ed.) 1968).
The Thum and Balbach systems further suffer from the disadvantage that the anode baskets need to be lined with fabric. This fabric traps the anode mud but also increases the cell voltage so that part of the stainless steel would dissolve as well as the silver.
Since some obsolete supersonic military aircraft contain approximately 300 lb. of silver, a new and econominal process is needed for its recovery. Subsonic military aircraft previously used do not generally contain sections of similar metal content. An exception is the flame cone assembly found on some jet engines.
It is therefore an object of the present invention to provide a method for recovering silver from stainless steel honeycomb sections brazed with silver based brazing compound which is substantially free of the disadvantages of the prior art.
Another object of the present invention is to recover silver from silver brazed stainless steel sections when the silver is present as about 5 to 30 weight percent of the sections.
A further object of the present invention is to provide a commercially successful economical process for recovering metals from silver brazed stainless steel sections of obsolete supersonic military aircraft.
Yet another object of the present invention is to provide a process using an anode basket that does not need to be lined with fabric so that the stainless steel sections are left undissolved but stripped of braze in the anode basket.